要實現一個Java復數類，你可以按照以下步驟進行：

1. 創建一個名為Complex的類，并在該類中聲明兩個私有變量，用于表示復數的實部和虛部。可以使用double類型變量來表示這兩個部分。

public class Complex {
    private double real;
    private double imaginary;
    
    // 構造方法、getter和setter等其他方法
}

2. 實現Complex類的構造方法，以便在創建Complex對象時初始化實部和虛部。

public Complex(double real, double imaginary) {
    this.real = real;
    this.imaginary = imaginary;
}

3. 提供getter和setter方法，用于獲取和設置實部和虛部的值。

public double getReal() {
    return real;
}

public void setReal(double real) {
    this.real = real;
}

public double getImaginary() {
    return imaginary;
}

public void setImaginary(double imaginary) {
    this.imaginary = imaginary;
}

4. 實現復數加法和乘法的方法。可以使用以下公式計算兩個復數的和和積：

   • 復數加法：(a + bi) + (c + di) = (a + c) + (b + d)i
   • 復數乘法：(a + bi) * (c + di) = (ac - bd) + (ad + bc)i

public Complex add(Complex other) {
    double realPart = this.real + other.real;
    double imaginaryPart = this.imaginary + other.imaginary;
    return new Complex(realPart, imaginaryPart);
}

public Complex multiply(Complex other) {
    double realPart = this.real * other.real - this.imaginary * other.imaginary;
    double imaginaryPart = this.real * other.imaginary + this.imaginary * other.real;
    return new Complex(realPart, imaginaryPart);
}

5. 可選：實現toString方法，用于以字符串形式表示復數。

@Override
public String toString() {
    if (imaginary >= 0) {
        return real + " + " + imaginary + "i";
    } else {
        return real + " - " + (-imaginary) + "i";
    }
}

這樣，你就可以使用這個Complex類來表示和操作復數了。例如：

Complex a = new Complex(2, 3);
Complex b = new Complex(4, -1);

Complex sum = a.add(b);
System.out.println("Sum: " + sum);

Complex product = a.multiply(b);
System.out.println("Product: " + product);

輸出結果為：

Sum: 6.0 + 2.0i
Product: 11.0 + 10.0i